The structural evolution of amorphous ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Fe}}_{\mathit{x}}$ with composition has been investigated. Implanted specimens with iron concentrations below and above x=0.2, where a structural transformation was previously reported for evaporated samples, have been studied by conversion-electron Mössbauer spectroscopy. Applying the model of Miedema and van der Woude for the isomer shift, a consistent description of our results and of those available from the literature (both from ion-implanted and coevaporated specimens) is given, which covers a wide composition range (0.001≤x≤0.750). It was concluded that three differentiated regions exist: a silicon-rich one where iron bears a strong covalent character in a continuous random network structure; an intermediate region where the covalent character decreases continuously at the iron sites, which are here proposed to have a local structure like the one existing in the intermetallic compound FeSi; and finally an iron-rich region where covalent effects are absent, supporting a dense-random-packing description of the amorphous structure.

• Received 4 October 1990

DOI:https://doi.org/10.1103/PhysRevB.44.4290